Sensor structures, systems and methods with improved integration and optimized footprint

ABSTRACT

Embodiments relate to sensors and more particularly to structures for and methods of forming sensors that are easier to manufacture as integrated components and provide improved deflection of a sensor membrane, lamella or other movable element. In embodiments, a sensor comprises a support structure for a lamella, membrane or other movable element. The support structure comprises a plurality of support elements that hold or carry the movable element. The support elements can comprise individual points or feet-like elements, rather than a conventional interconnected frame, that enable improved motion of the movable element, easier removal of a sacrificial layer between the movable element and substrate during manufacture and a more favorable deflection ratio, among other benefits.

TECHNICAL FIELD

The invention relates generally to sensors and more particularly tostructures for and methods of forming sensors comprising moveableelements, such as membranes or lamellas, that are easier to manufactureas integrated components and provide improved deflection of the membraneor lamella.

BACKGROUND

Sensors are commonly used in a variety of applications, includingelectronics, automotive and consumer goods, among others. Some types ofsensors comprise a membrane, lamella or other suitable structure thatflexes, deforms or otherwise moves in response to a physical quantity tobe sensed or measured. One example of such a sensor is a pressuresensor, which can sense or measure pressure related to a gas, fluid,mechanical or other force. The flexure, deformation and/or movement ofthe moveable portion of the sensor (e.g., the membrane, lamella or otherstructure) can be sensed by a variety of technologies, includingcapacitive, piezoresistive, piezoelectric, electromagnetic, optical orsome other technology, and the related pressure determined therefrom.For example, a pressure sensor can comprise a flexible membrane thatflexes or otherwise deforms when a pressure is present. The flexure ofthe membrane can be detected capacitively by an electrode arrangedproximate the membrane, as a capacitance between the membrane and theelectrode changes as the membrane sags or expands.

Regardless of type, sensors often operate as parts of larger systems andtherefore may be integrated within these systems. In some applications,such as automotive airbag sensors, a pressure sensor can be integratedwithin the airbag application-specific integrated circuit (ASIC). As theprocesses for manufacturing ASICs develop and evolve, it can bechallenging to integrate manufacture of the sensors with the ASICwithout increasing the complexity of or having to alter the fundamentalmanufacturing processes. For example, many ASICs are constructed usingCMOS (complementary metal-oxide-semiconductor) technologies, andintegrating pressure sensor construction into suitable CMOS processescan be complicated and/or expensive, sometimes requiring changes to theconventional processing steps or techniques or requiring additionalsteps. For example, one attempt to integrate pressure sensor structurecomprising a polycrystalline silicon lamella required at least five maskplanes and a complicated process for removing the sacrificial layerbetween the lamella and the substrate to enable the lamella to flex ormove and could not be successfully integrated in a CMOS process.

SUMMARY

Embodiments relate to sensors and more particularly to structures forand methods of forming sensors that are easier to manufacture asintegrated components and provide improved deflection of a sensormembrane, lamella or other movable element.

In an embodiment, a sensor device comprises a substrate; a plurality ofsupport elements spaced apart from each other and arranged on thesubstrate; and a moveable element supported on and spaced apart from thesubstrate by the plurality of support elements, wherein the moveableelement, the substrate and the plurality of support elements define acavity into which the moveable element can deflect in response to aphysical quantity to be sensed by the sensor device.

In an embodiment, a method comprises providing a substrate; providing amoveable element supported on the substrate by a plurality of supportelements spaced apart from one another; and sensing a physical quantityby a deflection of the moveable element toward the substrate into acavity defined by the substrate, the moveable element and the pluralityof support elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 is a side cross-sectional view of a conventional sensor.

FIG. 2 is a side cross-sectional view of a sensor according to anembodiment.

FIG. 3 is a top partially transparent view of a moveable element andsupport elements of a sensor according to an embodiment.

FIG. 4A is a simulation result of a sensor according to an embodiment.

FIG. 4B is a simulation result of a sensor according to an embodiment.

FIG. 4C is a simulation result of a sensor array according to anembodiment.

FIG. 4D is a simulation result of a conventional sensor.

FIG. 5 is a flowchart of a method of forming a sensor according to anembodiment.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

Embodiments relate to sensors and more particularly to structures forand methods of forming sensors that are easier to manufacture asintegrated components and provide improved deflection of a sensormembrane, lamella or other movable element. In embodiments, a sensorcomprises a support structure for a lamella, membrane or other movableelement. The support structure comprises a plurality of support elementsthat hold or carry the movable element. The support elements cancomprise individual points or feet-like elements, rather than aconventional interconnected frame, that enable improved motion of themovable element, easier removal of a sacrificial layer between themovable element and substrate during manufacture and a more favorabledeflection ratio, among other benefits.

Referring to FIG. 1, a sensor 10 is depicted. Sensor 10 comprises asubstrate 12, a lamella 14 and a cavity 16. Lamella 14 is supported by aframe 18 which extends around a perimeter of lamella 14 between lamella14 and shallow trench isolation (STI) portions 13 of substrate 12. Inone embodiment, sensor 10 comprises a pressure sensor, and lamella 14 ispressure-sensitive, moving (e.g., by flexing downwardly or upwardly) inresponse to changes in pressure. Sensor 10 can comprise another type ofsensor in other embodiments.

In embodiments, several mask planes (e.g., five or six in some cases)and a complicated process for removing the sacrificial layer belowlamella 14 to form cavity 16 are necessary in the manufacture of sensor10, making it difficult or impossible to integrate manufacture of sensor10 with conventional processing, such as CMOS. For example, asacrificial layer comprising, e.g., a sacrificial material that can bedry-etched, such as carbon, can be deposited on substrate 12 andstructured prior to lamella 14, comprising, e.g., polycrystallinesilicon, being deposited or formed on substrate 12 over the sacrificiallayer. This process results in step 20 of frame 18. After deposition oflamella 14, the sacrificial layer can be removed, such as by ashing andsubsequent removal of the material via small apertures formed in lamella14 in one embodiment, to form cavity 16, which enables lamella 14 tomove and flex in operation. Removal of the sacrificial layer in this way(i.e., via small apertures formed in lamella 14, such as near thecorners) severely limits lateral dimensions of sensor 10, as clearingwidths in such a scheme are finite.

Step 20 can be disadvantageous because it is a stress point, resultingin a bending movement of lamella 14 where lamella 14 meets frame 18.This bending movement can cause sagging of lamella 14 dependent on avariety of factors, including the geometry of sensor 10, stress, andtemperature in addition to the desired pressure such that the sagging isincluded in the pressure sensor characteristic data as an undesirable,non-linear factor.

In embodiments, sensor 10 is generally square, with lateral dimensionsof about 5 μm to about 15 μm (e.g., the width of sensor 10 in FIG. 1 isabout 10 μm and the length—the dimension into the page—is about 10 μm inone example embodiment). A size-related characteristic of sensor 10 isthe ratio of the maximum deflection of lamella 14 during pressurizationto the average deflection of lamella. In general, and for reasonsrelating to linearity and the production of sensor 10 (i.e., theformation of cavity 16), the maximum deflection should not exceed about10 percent of the height of cavity 16, which can lead to a larger andthicker lamella 14 that is undesirable because of size limitations andcost constraints. The average deflection, on the other hand, is relatedto the capacitive sensor signal. A configuration in which the ratio ofmaximum deflection to average deflection is as small as possibletherefore can be advantageous.

Referring to FIG. 2, another sensor 100 is depicted. Similar to sensor10 previously discussed, sensor 100 comprises a substrate 102, such as asemiconductor or other suitable material, and a moveable element 104,such as a lamella, membrane or other suitable structure. In contrastwith frame 18 of sensor 10, however, sensor 100 comprises a supportstructure comprising a plurality of support elements 122. Each supportelement 122 comprises a punctiform structure or “foot” arranged on anisolation trench portion 103 of substrate 102, spaced apart from andindependent of the other support elements. Though the size andconfiguration can vary, in embodiments each support element 122 isgenerally square-shaped and has a lateral dimension of less than about3,000 nm, such as lateral dimensions of about 500 nm by 500 nm and aheight of about 20 nm to about 400 nm, though support elements can belarger or smaller and/or have some other shape (e.g., round, triangular,oval, rectangular, hexagonal, some other single- or multi-sided shape,etc.) in other embodiments. For example, in one embodiment sensor 100 istriangularly shaped and comprises three support elements 122. A cavity106 separates and is defined by substrate 102 and moveable element 104.The height of support elements 122 defines the height of cavity 106(i.e., the distance between a bottom surface of moveable element 104 anda top surface of substrate 102), and the height can be in a range ofabout 20 nm to about 200 nm in some embodiments.

In one embodiment, portion 103 comprises oxide or another suitablematerial, and support elements 122, like moveable element 104, cancomprise silicon, such as polycrystalline silicon in one embodiment. Thematerials, dimensions and other characteristics of various elementsdiscussed herein are merely examples and can vary from that which isdepicted (which is generally not scale) and discussed in otherembodiments, without limitation unless otherwise mentioned.

While a single sensor 100 can be formed on substrate 102, in someembodiments arrays of sensors 100 will be formed on substrate 102. FIG.3 depicts a top view of such an array 101 of sensors 100, with moveableelement 104 in transparency in order to see support elements 122underneath. The number of sensors 100 of any array 101 can vary fromthat depicted in FIG. 3 and, practically speaking, can be significantlylarger than the thirty sensors 100 depicted but can also be smaller. Forexample, in one embodiment array 101 comprises 400 sensors 100 arrangedin a 10×40 configuration. In embodiments, the number of support element122 is greater than 20, such as greater than 50 in some embodiments, andgreater than 100 in still other embodiments.

Each sensor 100 is generally square-shaped and supported by four supportelements 122, though other configurations (i.e., different sensor shapesand/or more or fewer support elements 122) can be implemented in otherembodiments. Thus, in FIG. 3, each sensor 100 is defined, in part, bythe four support elements 122 supporting a portion of moveable element104. Support elements 122 can be in arranged in a regular manner in someembodiments, such as in a regular matrix. In some embodiments, eachsupport element 122 can have the same distance to an adjacent supportelement 122, and this distance can be in a range of about 2 μm to about20 μm in embodiments, though this distance can also be greater orsmaller in other embodiments.

In some embodiments, support elements 122 can be arranged in anon-regular manner, i.e., with varying distances to one or more adjacentsupport elements 122. This can, for example increase a measurement rangeor tailor a sensor behavior since a support element 122 having a greaterdistance to the next support element 122 may provide a highersensitivity, and shorter distances to the next support element 122 mayprovide the capability to measure at higher pressures. For example, thedistances between adjacent support elements 122 can be varied inembodiments in a range of about 2 μm to about 20 μm, and can vary fromsupport element to support element. The distances also can be greater orsmaller in other embodiments,

For regular arrangements as well as for non-regular arrangements, theselection of the distances between adjacent support elements 122 can beused to specifically tailor the sensors to one or more requirements ofthe sensor or application. For example, high pressure sensors can bedesigned to have smaller distances between adjacent support elements122, and low pressure sensors can be designed to have greater distancesbetween adjacent support elements 122. Wide measurement range sensorscan be designed to have a wide variation of the distances betweenadjacent support elements across the sensor.

In embodiments, additional support elements 122 can be implemented inarray 101 in areas of increased tensile stress or where additionalsupport is otherwise desired or required. For example, in someembodiments additional support elements 122 are provided along theperimeter or outer edges of array 101, or along some interior part orportion of the array. Moveable element 104 can comprise a singlecontiguous structure coupled to, applied on or formed with the pluralityof support elements 122 in various embodiments. Each sensor 100 alsocomprises a corresponding portion of substrate 102 (see FIG. 2) oppositemoveable element 104, as well as other elements not specificallydepicted or visible, such as electrodes, wires, pads, control circuitryand other components.

For either a single sensor 100 or array 101 of sensors 100, numerousadvantages are provided in embodiments. First, the removal of thesacrificial layer between substrate 102 and moveable element 104 is madeeasier via much wider and easier to access sides or edges of sensor 100or array 101, which are open and are not closed off by frame 18 as inFIG. 1, though after removal of the sacrificial layer can be sealed by adielectric layer or other layer or structure. This removes constraintson sensor size and configuration, which previously were necessary inorder to ensure that the entire sacrificial layer could be removed.

Additionally, the ratio of maximum deflection of moveable element 104 toaverage deflection of moveable element 104 is improved. In one example,the ratio for sensor 10 of FIG. 1 is about 3.5, whereas the same ratiofor sensor 100 of FIG. 2 or 3 is reduced to about 1.65, which is asignificant improvement. FIGS. 4A and 4B depict simulation results for asensor 100 within an array, and FIG. 4C for an array 101, with one barof pressure applied without intrinsic stress. For comparison, simulationresults for sensor 10 of FIG. 1 are also included in FIG. 4D. Acomparison of FIGS. 4A and 4D shows improved deflection in theembodiment of FIG. 4A. The central area of maximum deflection ofmoveable element 104 (about 4.7 nm in this simulation, in which sensor100 is about 8 μm by 8 μm) is larger and differently shaped than that oflamella 14 of FIG. 4D.

While the improved ratio can provide advantages with respect to sensorperformance, such as increased linearity and/or sensitivity, thecombination of these two advantages enables structuring and formation ofadvantageous sensors 100 and sensor arrays 101 that do not require thepreviously necessary clearing holes that limited size and configurationand make integration of a sensor 100 or array 101 of sensors 100 withother structures and processes, including CMOS processing, possible.

Thus, in one embodiment and referring to flowchart 500 of FIG. 5, asubstrate is provided at 502. At 504, the cavity is structured onsubstrate, and at 506 the support elements are formed on the substrate.At 508, the moveable element is coupled to the structure by the supportelements. In some embodiments, 506 and 508 are carried out jointly, suchas by deposition of a single layer that forms the support elements andthe moveable element. This is illustrated by the dashed lines in FIG. 5.At 510, a dielectric layer is applied between the substrate and themoveable element to seal the cavity. This process, its contents and/orthe order of the various actions can vary according to an embodimentand/or a process used to form a circuit (e.g., ASIC) or structure withor in which sensor 100 or array 101 is integrated.

For example, in one embodiment following a similar process to thatillustrated in FIG. 5, deposition and structuring of a sacrificial layer(e.g., to form the cavity) is carried out, including forming holes forthe support elements. Next, a layer, such as polysilicon, is formed andstructured to form the support elements and the moveable element. Then,an oxide layer, such as a high density plasma (HDP) oxide in oneembodiment, is applied for evacuation and to form a lateral sealinglayer.

Sensor 100 and/or array 101 of sensors 100 can comprise pressure sensorsin embodiments. In operation and in response to a pressure applied orotherwise present, moveable element 104 moves, such as by sagging,flexing or otherwise deflecting, into cavity 106 and toward substrate102. This movement can be sensed, such as by a change in capacitance asthe distance separating moveable element 104 and substrate 102 changes,and from that change in capacitance the pressure applied or otherpresent can be determined. In other embodiments, sensor 100 and/or array101 can comprise a sensor other than a pressure sensor (e.g.,acceleration, force, etc.) and/or can rely on an effect other cancapacitance (e.g., piezoresistive, piezoelectric, electromagnetic,optical or some other technology).

Various embodiments of systems, devices and methods have been describedherein. These embodiments are given only by way of example and are notintended to limit the scope of the invention. It should be appreciated,moreover, that the various features of the embodiments that have beendescribed may be combined in various ways to produce numerous additionalembodiments. Moreover, while various materials, dimensions, shapes,configurations and locations, etc. have been described for use withdisclosed embodiments, others besides those disclosed may be utilizedwithout exceeding the scope of the invention.

Persons of ordinary skill in the relevant arts will recognize that theinvention may comprise fewer features than illustrated in any individualembodiment described above. The embodiments described herein are notmeant to be an exhaustive presentation of the ways in which the variousfeatures of the invention may be combined. Accordingly, the embodimentsare not mutually exclusive combinations of features; rather, theinvention can comprise a combination of different individual featuresselected from different individual embodiments, as understood by personsof ordinary skill in the art. Moreover, elements described with respectto one embodiment can be implemented in other embodiments even when notdescribed in such embodiments unless otherwise noted. Although adependent claim may refer in the claims to a specific combination withone or more other claims, other embodiments can also include acombination of the dependent claim with the subject matter of each otherdependent claim or a combination of one or more features with otherdependent or independent claims. Such combinations are proposed hereinunless it is stated that a specific combination is not intended.Furthermore, it is intended also to include features of a claim in anyother independent claim even if this claim is not directly madedependent to the independent claim.

Any incorporation by reference of documents above is limited such thatno subject matter is incorporated that is contrary to the explicitdisclosure herein. Any incorporation by reference of documents above isfurther limited such that no claims included in the documents areincorporated by reference herein. Any incorporation by reference ofdocuments above is yet further limited such that any definitionsprovided in the documents are not incorporated by reference hereinunless expressly included herein.

For purposes of interpreting the claims for the present invention, it isexpressly intended that the provisions of Section 112, sixth paragraphof 35 U.S.C. are not to be invoked unless the specific terms “means for”or “step for” are recited in a claim.

What is claimed is:
 1. A sensor device comprising: a substrate; aplurality of support elements spaced apart from each other and arrangedon the substrate; and a moveable element supported on and spaced apartfrom the substrate by the plurality of support elements, wherein themoveable element, the substrate and the plurality of support elementsdefine a cavity into which the moveable element can deflect in responseto a physical quantity to be sensed by the sensor device.
 2. The sensordevice of claim 1, wherein the moveable element comprises a membrane ora lamella.
 3. The sensor device of claim 2, wherein the moveable elementcomprises silicon.
 4. The sensor device of claim 3, wherein the siliconcomprises polycrystalline silicon.
 5. The sensor device of claim 1,wherein the sensor device comprises a pressure sensor device, andwherein the physical quantity to be sensed is pressure.
 6. The sensordevice of claim 5, wherein the pressure is sensed by sensing acapacitance between the moveable element and the substrate.
 7. Thesensor device of claim 1, wherein the plurality of support elementscomprise punctiform structures.
 8. The sensor device of claim 7, whereina lateral dimension of a punctiform structure is less than about 3,000nanometers (nm).
 9. The sensor device of claim 8, wherein the punctiformstructure has lateral dimensions of about 500 nm by about 500 nm. 10.The sensor device of claim 1, wherein the sensor device comprises aplurality of sensors, each of the plurality of sensors comprising aplurality of support elements and a portion of the moveable elementsupported on that plurality of support elements.
 11. The sensor deviceof claim 10, wherein adjacent ones of the plurality of sensors have atleast one of the plurality of support elements in common.
 12. The sensordevice of claim 10, further comprising a sealing layer arranged betweenthe substrate and the moveable element along a perimeter of the sensordevice.
 13. The sensor device of claim 12, wherein the sealing layercomprises a dielectric layer.
 14. The sensor device of claim 1, whereinthe substrate comprises a plurality of isolation portions, and whereineach of the plurality of support elements is arranged on a respectiveone of the plurality of isolation portions.
 15. The sensor device ofclaim 1, wherein a ratio of maximum deflection of the moveable elementto average deflection of the moveable element is less than about
 2. 16.The sensor device of claim 1, wherein the moveable element and theplurality of support elements are integrally formed with one another.17. A method comprising: providing a substrate; providing a moveableelement supported on the substrate by a plurality of support elementsspaced apart from one another; and sensing a physical quantity by adeflection of the moveable element toward the substrate into a cavitydefined by the substrate, the moveable element and the plurality ofsupport elements.
 18. The method of claim 17, wherein sensing a physicalquantity further comprises sensing a capacitance between the substrateand the moveable element.
 19. The method of claim 17, wherein for eachof the plurality of support elements a distance to an adjacent one ofthe plurality of support elements is in a range of about 2 micrometers(μm) to about 20 μm.
 20. The method of claim 17, wherein the moveableelement comprises a silicon layer.